Although the present invention has useful application to numerous industrial and commercial uses, its principles may be best exemplified by reference to its use as shock absorber for automotive vehicles and its ability to dampen forces of substantial magnitude applied to the suspension components of a vehicle.
I have previously devised a shock absorbing system in which a piston member is axially movable in an enclosed cylinder, and a slide member is disposed in the piston member and adapted to be movable across one or more bypass openings or orifices in response to changes in fluid pressure so as to regulate the bypass or flow of fluid from one side of the piston to the other in absorbing forces and dampening vibrations applied to the piston. Here, reference is made to my prior U.S. Pat. No. 3,896,908 for SHOCK ABSORBING APPARATUS. As disclosed therein, the slide member within the piston is disposed in an internal chamber and is normally disposed in predetermined relation to the bypass orifices. The internal chamber of the piston is in fluid communication with the fluid in the cylinder so that movement of the piston will exert increased pressure on the fluid at one end of the cylinder causing it to flow into the internal chamber of the piston and exert a pressure against one side of the slide member. The bypass orifices are positioned along the inner wall of the internal chamber and have selectively variable cross-sectional opening sizes and configurations to determine the degree of pressure resistance to movement of the piston irrespective of the speed of movement of the piston. This was found to achieve substantial advances in the present art of shock absorbers where fixed size orifices are primarily responsive to piston velocity or speed. In further explanation of the prior art employing fixed size orifices, it is acknowledged that fluid flow through a fixed orifice size results in an exponential curve. Thus, there is a disproportionately low pressure-to-flow relationship at low velocities and a disproportionately high pressure-to-flow relationship at high velocities. Shock absorbers employing a fixed size piston orifice, or a multiplicity of open and closed orifices, also employ relief or blow-off valves in the base of the pressure cylinder and at the piston. These blow-off valves, to prevent high pressure damage to the device, also have fixed size orifices. Again recognizing the exponential curve of a fixed orifice, the blow-off valve is set at a low limit effectively limiting the overall pressure and dampening capability of the device. Without a blow-off valve the conventional shock absorber would destruct under severe impacts, such as, those resulting from chuck holes or severe jolts. The further demand for a low limit setting and maximum flow is realized in considering the effect of low temperature and increased fluid viscosity.
The fluttering pressure responses and abrupt pressure peaks resulting from the opening and closing of the blow-off valves contribute to shock absorber noises, fluid cavitation and foaming, increased parts damage and wear both of the shock absorber and suspension components. Additionally, the functional limitation of the shock absorber limits suspension and vehicular control. Recognizing that fixed size orifices produce exponential curves explains the degree of compromise and limitation imposed when the end product either requires a linear response, a directly proportionate response, or a variable pressure speed response that must pass both above and below the linear curve.
In accordance with the teachings of my hereinbefore referred to patent, a predetermined force-speed performance curve can be achieved by the advancement of a slide member across a shaped orifice in response to pressure wherein the slide member is biased to oppose the fluid force within a piston housing. With the preferred laminar fluid flow and the chosen depth of the orifice remaining constant, a predetermined pressure drop across the orifice, in response to the application of a given force on the sliding member, is a direct result of the orifice width adjacent to the sliding member. While the principles of that invention still hold true, it is highly desirable to devise a shock absorber in which predetermined force-speed characteristics can be established via the selection of controlled orifice-sized shapes working in cooperation with an axial slide member which is extremely simplified in construction, employs a minimum number of parts, is operable over the widest possible speed and force ranges and permits ready interchangeability of orifice sizes while maintaining the closest possible control over its performance.